Thrombotic microangiopathy, hemolytic uremic syndrome, and thrombotic thrombocytopenic purpura. Ruggenenti P, Noris M, Remuzzi G. Kidney International 2001;60(3):831-846.

The term thrombotic microangiopathy (TMA) defines a lesion of vessel wall thickening (mainly arterioles or capillaries), intraluminal platelet thrombosis, and partial or complete obstruction of the vessel lumina. Depending on whether renal or brain lesions prevail, two pathologically indistinguishable but somehow clinically different entities have been described: the hemolytic uremic syndrome (HUS) and the thrombotic thrombocytopenic purpura (TTP). Outcome is usually good in childhood, Shiga toxin-associated HUS, which usually recovers spontaneously and does not require plasma therapy. In contrast, renal and neurological sequelae are more frequently reported in adult, atypical, and familial forms of HUS and in TTP. Plasma exchange or infusion should always be tried in adult HUS/TTP to minimize the risk of death or long term sequelae. Platelet count and serum LDH are the most sensitive markers for monitoring the response to plasma therapy, and treatment should be continued until complete disease remission is achieved. However, no clinical parameter predicts the duration for plasma therapy and the decision to stop or continue plasma therapy is empirical. Prompt exacerbation of disease activity requires resumption of daily plasma therapy, and while it is common after treatment discontinuation, discontinuation is the only way to know whether a durable remission has been achieved. Plasma infusion or exchange is the only treatment of proven efficacy. Bilateral nephrectomy and splenectomy may serve as rescue therapies in very selected cases of plasma resistant HUS or recurrent TTP, respectively. Other treatments which might be effective include prednisone, which is possibly effective in mild, adult forms and is of questionable effectiveness as additional therapy in poor responders to plasma infusion or exchange, and gamma globulin and vincristine, which are of unproven efficacy.